Some suggestions -
1) Clean the pin header the LCD plugs into. Use 90% alcohol.
2) Make sure contrast pot R6 is cleaned and adjusted.
3) Make sure you are issuing start command to LCD to initialize it.
Are you able to see all the boxes on both the lines of display? If that's the case the contrast is too high. Pls adjust the R6 potentiometer named LCD contrast until it dims.
Something similar happens ocacionally with my CY8CKIT-50 (non LP version)
When I plug it to the USB port the first line of the LCD will show boxes while the second line is still off. It hapens ocacionally so i just unplug it and plug it again and everything works.
after some investigation, it turns out that in such ocations the PSOC5 chip in it is not running properly and has all its pins in open drain outputs (as indicated by the powered LEDs on the pins )